1. Field of the Invention
The present invention relates to DC motor systems and, more particularly, to dual speed DC motor systems.
2. Description of the Related Art
Dual speed DC motor systems are used in a variety of applications including automotive systems. Conventional dual speed DC motor systems include either three brushes or the standard two brushes along with an electronic controller, such as a pulse width modulation controller. A problem with the typical three brush systems used in dual speed applications is that they produce a biased performance when switching between clockwise rotational direction and counterclockwise rotational direction. For example, the motor speed in the clockwise direction may be substantially different from the motor speed in the counterclockwise direction, which is undesirable in many applications. Another problem with three brush systems is that the difference between the low speed and the high speed may be less than desired. The use of an electronic controller is also a sub-optimal solution because of the cost of the controller and the space occupied thereby.
What is needed in the art is a dual speed DC motor system that does not require an electronic controller, that has substantially the same performance in either rotational direction, and that has an increased speed differential between the low speed and the high speed.